Abstract: In recent years evidence has been accumulating that personalities are not only found in humans but also in a wide range of other animal species. Individuals differ consistently in their behavioural tendencies and the behaviour in one context is correlated with the behaviour in multiple other contexts. From an adaptive perspective, the evolution of animal personalities is still a mystery, because a more flexible structure of behaviour should provide a selective advantage. Accordingly, many researchers view personalities as resulting from constraints imposed by the architecture of behaviour (but see ref. 12). In contrast, we show here that animal personalities can be given an adaptive explanation. Our argument is based on the insight that the trade-off between current and future reproduction often results in polymorphic populations in which some individuals put more emphasis on future fitness returns than others. Life-history theory predicts that such differences in fitness expectations should result in systematic differences in risk-taking behaviour. Individuals with high future expectations (who have much to lose) should be more risk-averse than individuals with low expectations. This applies to all kinds of risky situations, so individuals should consistently differ in their behaviour. By means of an evolutionary model we demonstrate that this basic principle results in the evolution of animal personalities. It simultaneously explains the coexistence of behavioural types, the consistency of behaviour through time and the structure of behavioural correlations across contexts. Moreover, it explains the common finding that explorative behaviour and risk-related traits like boldness and aggressiveness are common characteristics of animal personalities.

Abstract: Individuals consistently differ in behavioural phenotypes. Here we examine the interaction between behavioural phenotype and response to social context during novel object exploration in a neophobic corvid species, the raven (Corvus corax). The presence of conspecifics tends to encourage object exploration and learning but may also delay or even inhibit exploratory behaviour. Factors such as individual differences in response to social context may determine whether the presence of a conspecific facilitates or inhibits approach to novel objects. We confronted eleven six-month-old hand-raised ravens with novel objects, both individually and in dyadic combinations. We defined individuals as “fast” and “slow” explorers on the basis of their approach latency to novel objects when tested individually. The presence of a conspecific delayed the approach of fast birds to novel objects. Slow birds, in contrast, approached the novel objects with lower latencies and spent more time close to them when in dyads with fast siblings than when alone. The individuals" approach behaviour seemed to determine whether social context facilitated or delayed exploratory behaviour. This may contribute to explaining ambiguous results concerning the effects of social context in previous studies.